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聊聊dubbo的LRUCache

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本文主要研究一下dubbo的LRUCache

LRUCache

dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/utils/LRUCache.java

public class LRUCache<K, V> extends LinkedHashMap<K, V> {

    private static final long serialVersionUID = -5167631809472116969L;

    private static final float DEFAULT_LOAD_FACTOR = 0.75f;

    private static final int DEFAULT_MAX_CAPACITY = 1000;
    private final Lock lock = new ReentrantLock();
    private volatile int maxCapacity;

    public LRUCache() {
        this(DEFAULT_MAX_CAPACITY);
    }

    public LRUCache(int maxCapacity) {
        super(16, DEFAULT_LOAD_FACTOR, true);
        this.maxCapacity = maxCapacity;
    }

    @Override
    protected boolean removeEldestEntry(java.util.Map.Entry<K, V> eldest) {
        return size() > maxCapacity;
    }

    @Override
    public boolean containsKey(Object key) {
        lock.lock();
        try {
            return super.containsKey(key);
        } finally {
            lock.unlock();
        }
    }

    @Override
    public V get(Object key) {
        lock.lock();
        try {
            return super.get(key);
        } finally {
            lock.unlock();
        }
    }

    @Override
    public V put(K key, V value) {
        lock.lock();
        try {
            return super.put(key, value);
        } finally {
            lock.unlock();
        }
    }

    @Override
    public V remove(Object key) {
        lock.lock();
        try {
            return super.remove(key);
        } finally {
            lock.unlock();
        }
    }

    @Override
    public int size() {
        lock.lock();
        try {
            return super.size();
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void clear() {
        lock.lock();
        try {
            super.clear();
        } finally {
            lock.unlock();
        }
    }

    public int getMaxCapacity() {
        return maxCapacity;
    }

    public void setMaxCapacity(int maxCapacity) {
        this.maxCapacity = maxCapacity;
    }

}

LRUCache继承了LinkedHashMap，其initialCapacity为16，maxCapacity默认是1000；它覆盖了removeEldestEntry方法，当size()大于maxCapacity时返回true；它还声明了一个ReentrantLock，对containsKey、get、put、remove、size、clear方法进行了加锁操作

实例

dubbo-2.7.2/dubbo-common/src/test/java/org/apache/dubbo/common/utils/LRUCacheTest.java

public class LRUCacheTest {
    @Test
    public void testCache() throws Exception {
        LRUCache<String, Integer> cache = new LRUCache<String, Integer>(3);
        cache.put("one", 1);
        cache.put("two", 2);
        cache.put("three", 3);
        assertThat(cache.get("one"), equalTo(1));
        assertThat(cache.get("two"), equalTo(2));
        assertThat(cache.get("three"), equalTo(3));
        assertThat(cache.size(), equalTo(3));
        cache.put("four", 4);
        assertThat(cache.size(), equalTo(3));
        assertFalse(cache.containsKey("one"));
        assertTrue(cache.containsKey("two"));
        assertTrue(cache.containsKey("three"));
        assertTrue(cache.containsKey("four"));
        cache.remove("four");
        assertThat(cache.size(), equalTo(2));
        cache.put("five", 5);
        assertFalse(cache.containsKey("four"));
        assertTrue(cache.containsKey("five"));
        assertTrue(cache.containsKey("two"));
        assertTrue(cache.containsKey("three"));
        assertThat(cache.size(), equalTo(3));
    }

    @Test
    public void testCapacity() throws Exception {
        LRUCache<String, Integer> cache = new LRUCache<String, Integer>();
        assertThat(cache.getMaxCapacity(), equalTo(1000));
        cache.setMaxCapacity(10);
        assertThat(cache.getMaxCapacity(), equalTo(10));
    }
}

这里验证了LRU的基本逻辑以及maxCapacity

小结

LRUCache继承了LinkedHashMap，其initialCapacity为16，maxCapacity默认是1000；它覆盖了removeEldestEntry方法，当size()大于maxCapacity时返回true；它还声明了一个ReentrantLock，对containsKey、get、put、remove、size、clear方法进行了加锁操作